IL4 and Friedreich ataxia: PI3K−/− mice failed to develop FA in our FA model, which were attributed to a deficiency of mast cells in the intestine, because: 1) mast cells can promote T-cell migration by producing chemokines [25], [26], 2) mast cell products can promote dendritic cells to acquire a Th2 cell-inducing phenotype [2], [27], and 3) mast cells themselves can produce Th2 cytokines, such as IL-4, 5 and 13 [2], [25].